Analysis of a spectrum produced by an excited sample of material can yield information about the elemental composition of the sample, including relative concentrations of constituent elements. Such analyses are performed in many contexts, including identifying and segregating metal types in metal recycling facilities, and quality control testing in factories and forensic work. In some spectrometric systems, direct reading photomultiplier tube (PMT) systems use multiple PMTs installed at the wavelengths of analytical interest, often covering only a small fraction of the spectrum (typically, less than a few percent of the spectrum from 130 nm to 500 nm).
In some contexts, time-resolution of a spectrum or analysis of a temporal sequent of the spectrum can provide additional or more accurate information about the composition of the sample than would otherwise be obtained.
Conventional two-dimensional charge-coupled devices (CCDs) are sometimes used to capture time-resolved spectral data, subject, however, to limitations of time resolution that preclude utility in certain applications. Such a CCD device includes light-sensitive pixels arranged in rows and columns. In one mode of operation, all but one row of pixels may be masked, so only the one unmasked row is exposed to light. A spectrum is projected on the exposed row of CCD pixels, such that each pixel is exposed to a different portion of the spectrum. Photogenerated charges accumulate under one or more of the exposed pixels. Periodically, the charges stored in all the rows are moved (shifted) to respective adjacent rows. That is, charges in the exposed pixels are moved to the first masked row, charges in the first masked row are moved to the second masked row, etc. Moving the charges out of the exposed row clears the charges from the pixels in that row. Charges in the last row are read out of the device. This architecture yields relatively poor signal-to-noise characteristics and does not facilitate rapid cycling of an imaging device, because charges accumulated in any exposed pixel must move through all the pixels of the corresponding column before the charges can be read out.